Optical device and driving method thereof

ABSTRACT

An optical device according to the embodiment of the inventive concept includes a waveguide path including a light generation region, a wavelength variable region, and a light modulation region, a first light waveguide layer provided in the light generation region to generate light, a second light waveguide layer provided in the wavelength variable region and connected to the first light waveguide layer, a ring-shaped third light waveguide layer provided in the light modulation region and connected to the second light waveguide layer, and first and second light modulation electrodes spaced apart from each other with the light modulation region therebetween. Here, the first light modulation electrode, the third light waveguide layer, and the second light modulation electrode vertically overlap each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35U.S.C. § 119 of Korean Patent Application Nos. 10-2018-0117236, filed onOct. 1, 2018, and 10-2019-0086334, filed on Jul. 17, 2019, the entirecontents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure herein relates to an optical device and a drivingmethod thereof. More particularly, the present disclosure herein relatesto an optical device including a wavelength variable region and a lightmodulation region and a driving method thereof.

An optical device integrated with a wavelength variable light source anda light intensity modulator is used for a wavelength divisionmultiplexing (WDM) system, and recently used as a light source of eachof a next generation-passive optical network (NG-PON) and a mobilefront-haul network.

Typically, an intensity modulator of the wavelength variable lightsource is integrated with an electro-absorption modulator (EAM) or aMach-Zehnder modulator (MZM).

SUMMARY

The present disclosure provides an optical device for emitting lighthaving a constant light modulation characteristic.

An embodiment of the inventive concept provides an optical deviceincluding: a waveguide path including a light generation region, awavelength variable region, and a light modulation region; a first lightwaveguide layer provided in the light generation region to generatelight; a second light waveguide layer provided in the wavelengthvariable region and connected to the first light waveguide layer; aring-shaped third light waveguide layer provided in the light modulationregion and connected to the second light waveguide layer; and first andsecond light modulation electrodes spaced apart from each other with thelight modulation region therebetween. Here, the first light modulationelectrode, the third light waveguide layer, and the second lightmodulation electrode vertically overlap each other.

In an embodiment, the optical device may further include gratingsprovided in the wavelength variable region.

In an embodiment, the second light waveguide layer may extend in a firstdirection, and the gratings may be arranged in the first direction.

In an embodiment, the optical device may further include an ohmic layerdisposed between the first light modulation electrode and the lightmodulation region.

In an embodiment, the optical device may further include a wavelengthconversion part disposed on the wavelength variable region.

In an embodiment, the wavelength conversion part may include a heatingelement.

In an embodiment, a peak wavelength of the light may be converted from afirst wavelength to a second wavelength by the wavelength conversionpart, a difference between the first wavelength and the secondwavelength may be defined as a first wavelength difference, a freespectral range (FSR) of the light emitted from the light modulationregion may be defined as a second wavelength difference, and an integermultiple of the second wavelength difference may be the same as thefirst wavelength difference.

In an embodiment, the second wavelength difference may satisfy amathematical equation below:second wavelength difference=c/nL  [Mathematical equation]

In an embodiment of the inventive concept, a method for driving anoptical device, the method including: generating light in a lightgeneration region of a waveguide path; converting a peak wavelength ofthe light in a wavelength variable region of the waveguide path, whereinthe peak wavelength of the light is converted from a first wavelength toa second wavelength; and modulating the light in a light modulationregion of the waveguide path. Here, a difference between the firstwavelength and the second wavelength is defined as a first wavelengthdifference, a free spectral range (FSR) of the modulated light isdefined as a second wavelength difference, and an integer multiple ofthe second wavelength difference is the same as the first wavelengthdifference.

In an embodiment, the modulating of the light in the light modulationregion may include modulating the light having a wavelength converted inthe wavelength variable region by using a ring-shaped light waveguidelayer in the light modulation region.

In an embodiment, the modulating of the light in the light modulationregion may include changing a refractive index of each of the lightmodulation region and the ring-shaped light waveguide layer by using anelectrode vertically overlapping the ring-shaped light waveguide layer.

In an embodiment, the second wavelength difference may satisfy amathematical equation below:second wavelength difference=c/nL  [Mathematical equation]

In an embodiment, the converting of the peak wavelength of the light inthe wavelength variable region may include converting the peakwavelength of the light by using a wavelength conversion part providedon the wavelength variable region.

In an embodiment, the wavelength conversion part may include a heatingelement.

In an embodiment, the wavelength conversion part may include an ohmiclayer and an electrode.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings are included to provide a furtherunderstanding of the inventive concept, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the inventive concept and, together with thedescription, serve to explain principles of the inventive concept. Inthe drawings:

FIG. 1A is a plan view illustrating an optical device according to anembodiment of the inventive concept;

FIG. 1B is a cross-sectional view taken along line A-A′ of FIG. 1A;

FIG. 1C is a cross-sectional view taken along line B-B′ of FIG. 1A;

FIG. 1D is a view for explaining a third light waveguide layer indetail;

FIG. 2A is a view representing a light intensity of first light;

FIG. 2B is a view representing a light intensity of second light;

FIG. 3A is a view representing a light intensity spectrum of the firstlight;

FIG. 3B is a view representing a transmission ratio between the firstlight and the second light;

FIG. 4 is a view representing a simulation result of a transmissionratio according to a specific condition;

FIG. 5A is a plan view illustrating an optical device according to anembodiment of the inventive concept;

FIG. 5B is a cross-sectional view taken along line A-A′ of FIG. 5A;

FIG. 6A is a plan view illustrating an optical device according to anembodiment of the inventive concept;

FIG. 6B is a cross-sectional view taken along line A-A′ of FIG. 6A;

FIG. 7 is a cross-sectional view of an optical device according to anembodiment of the inventive concept;

FIG. 8A is a plan view illustrating an optical device according to anembodiment of the inventive concept; and

FIG. 8B is a cross-sectional view taken along line A-A′ of FIG. 8A.

DETAILED DESCRIPTION

Advantages and features of the present invention, and implementationmethods thereof will be clarified through following embodimentsdescribed with reference to the accompanying drawings. The presentinvention may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the concept of theinvention to those skilled in the art. Further, the present invention isonly defined by scopes of claims. Like reference numerals refer to likeelements throughout.

In the following description, the technical terms are used only forexplaining a specific exemplary embodiment while not limiting thepresent disclosure. The terms of a singular form may include pluralforms unless referred to the contrary. The meaning of “include,”“comprise,” “including,” or “comprising,” specifies a property, aregion, a fixed number, a step, a process, an element and/or a componentbut does not exclude other properties, regions, fixed numbers, steps,processes, elements and/or components. Hereinafter, exemplaryembodiments will be described in detail with reference to theaccompanying drawings.

FIG. 1A is a plan view illustrating an optical device according to anembodiment of the inventive concept. FIG. 1B is a cross-sectional viewtaken along line A-A′ of FIG. 1A. FIG. 1C is a cross-sectional viewtaken along line B-B′ of FIG. 1A. FIG. 1D is a view for explaining athird light waveguide layer in detail.

Referring to FIGS. 1A, 1B, 1C, and 1D, the optical device according toan embodiment of the inventive concept may include a waveguide path 100.

The waveguide path 100 may include a lower clad layer 110, an upper cladlayer 120, and light waveguide layers 210, 220, 230, and 240. The lowerclad layer 110 may include an n-type semiconductor material. The upperclad layer 120 may include a p-type semiconductor material. For example,the waveguide path 100 may include InP or AlGaAs.

The waveguide path 100 may include a light generation region RG1, awavelength variable region RG2, and a light modulation region RG3. Thelight generation region RG1, the wavelength variable region RG2, and thelight modulation region RG3 may be sequentially arranged in a firstdirection D1.

The first to fourth light waveguide layers 210, 220, 230, and 240 may beprovided in the waveguide path 100. The first to fourth light waveguidelayers 210, 220, 230, and 240 may be provided between the lower cladlayer 110 and the upper clad layer 120. In terms of a cross-section inFIG. 1B, the lower clad layer 110, the first to fourth light waveguidelayers 210, 220, 230, and 240, and the upper clad layer 120 may besequentially arranged in a second direction D2. The second direction D2may be perpendicular to the first direction D1. Each of the first tofourth light waveguide layers 210, 220, 230, and 240 may have arefractive index greater than that of the waveguide path 100.

The first light waveguide layer 210 may be provided in the lightgeneration region RG1. The first light waveguide layer 210 may have astick or bar shape extending in the first direction D1. The first lightwaveguide layer 210 may contain an intrinsic semiconductor material. Thefirst light waveguide layer 210 may include materials having the samecompound composition and/or the same band gap as each other. The firstlight waveguide layer 210 may have a multiple quantum well (MQW)structure. The first light waveguide layer 210 may be an active layer.The active layer may generate optical gain. For example, the first lightwaveguide layer 210 may include InGaAsP, InGaAs, InGaAlAs, or GaAs.

The second light waveguide layer 220 may extend until the lightmodulation region RG3 from the wavelength variable region RG2. Thesecond light waveguide layer 220 may have a stick or bar shape extendingin the first direction D1. The second light waveguide layer 220 may beconnected to the first light waveguide layer 210.

The third light waveguide layer 230 may be provided in the lightmodulation region RG3. The third light waveguide layer 230 may have aring shape having a central axis that is parallel to the seconddirection D2. The third light waveguide layer 230 may be connected tothe second light waveguide layer 220. The second light waveguide layer220 and the third light waveguide layer 230 may have the same width andthickness as each other.

The fourth light waveguide layer 240 may be provided in the lightmodulation region RG3. The fourth light waveguide layer 240 may have astick or bar shape extending in the first direction D1. The fourth lightwaveguide layer 240 may be connected to the third light waveguide layer230. The third light waveguide layer 230 and the fourth light waveguidelayer 240 may have the same width and thickness as each other.

Each of the second to fourth light waveguide layers 220, 230, and 240may include an intrinsic semiconductor. The second to fourth lightwaveguide layers 220, 230, and 240 may include materials having the samecompound composition and/or the same band gap as each other. The secondto fourth light waveguide layers 220, 230, and 240 may be passivelayers. The passive layers may not generate optical gain. Each of thesecond to fourth light waveguide layers 220, 230, and 240 may includeInGaAsP, InGaAs, InGaAlAs, or GaAs.

The optical device according to an embodiment of the inventive conceptmay further include a first light generation electrode 310, a firstohmic layer 320, and a second light generation electrode 330.

The first ohmic layer 320 contacting the upper clad layer 120 in thelight generation region RG1 may be provided, and the first lightgeneration electrode 310 may be provided on the first ohmic layer 320.The second light generation electrode 330 contacting the lower cladlayer 110 in the light generation region RG1 may be provided. The secondlight generation electrode 330 may have a plate shape. That is, thesecond light generation electrode 330 may cover the entire lower cladlayer 110 in the light generation region RG1. Also, unlike asillustrated, the second light generation electrode 330 may extend fromthe light generation region RG1 to the light modulation region RG3.Here, the second light generation electrode 330 may cover the entirelower clad layer 110 in the light generation region RG1, the wavelengthvariable region RG2, and the light modulation region RG3. The first andsecond light generation electrodes 310 and 330 may be attached to eachother with the first ohmic layer 320, the upper clad layer 120, thefirst light waveguide layer 210, and the lower clad layer 110therebetween. The first light generation electrode 310, the first ohmiclayer 320, and the second light generation electrode 330 may overlapperpendicularly to each other (i.e., in the second direction D2). Aportion of the first light generation electrode 310, a portion of thefirst ohmic layer 320, and a portion of the second light generationelectrode 330 may overlap perpendicularly to the first light waveguidelayer 210.

Each of the first and second light generation electrodes 310 and 330 mayinclude at least one of gold, silver, copper, aluminum, platinum,tungsten, titanium, tantalum, molybdenum, indium, nickel, chrome, ormagnesium. The first ohmic layer 320 may include a p-type semiconductormaterial. For example, the first ohmic layer 320 may include InGaAs orGaAs.

The optical device according to an embodiment of the inventive conceptmay further include an insulation layer 500, a wavelength conversionpart WV, and gratings 420.

The insulation layer 500 may cover may cover the upper clad layer 120 inthe wavelength variable region RG2 and the light modulation region RG3.The insulation layer 500 may include a silicon oxide or a siliconnitride.

The wavelength conversion part WV may be provided on the insulationlayer 500 disposed on the wavelength variable region RG2. The wavelengthconversion part WV may include a heating element 410 and heating pads411. The heating element 410 may extend in the first direction D1. Theheating pads 411 may be connected to both ends of the heating element410. For example, the heating element 410 may include a nickel-chrome(Ni—Cr) alloy, platinum (Pt), or titanium (Ti). For example, each of theheating pads 411 may include metal.

The gratings 420 may be provided in the lower clad layer 110 in thewavelength variable region RG2 or the upper clad layer 120 in thewavelength variable region RG2. The gratings 420 may be spaced apartfrom each other in the first direction DR1. The gratings 420 may bearranged at a constant distance in the first direction D1. The gratings420 may be Bragg gratings.

The heating element 410, the second light waveguide layer 220, and thegratings 420 may vertically overlap each other.

The optical device according to an embodiment of the inventive conceptmay further include a first light modulation electrode 610, an electrodepad 611, a second ohmic layer 620, and a second light modulationelectrode 630.

The second ohmic layer 620 contacting the upper clad layer 120 in thelight modulation region RG3 may be provided, and the first lightmodulation electrode 610 may be provided on the second ohmic layer 620.The second light modulation electrode 630 contacting the lower cladlayer 110 in the light modulation region RG3 may be provided. The firstand second light modulation electrodes 610 and 630 may be attached toeach other with the second ohmic layer 620, the upper clad layer 120,the third light waveguide layer 230, and the lower clad layer 110therebetween.

In terms of a planar view according to FIG. 1A, each of the first lightmodulation electrode 610 and the second ohmic layer 620 may have a ringshape having opened one side. In other words, in terms of the planarview according to FIG. 1A, each of the first light modulation electrode610 and the second ohmic layer 620 may have a C-shape. The second lightmodulation electrode 630 may have a plate shape. That is, the secondlight modulation electrode 630 may cover the entire lower clad layer 110in the light modulation region RG3. The first light modulation electrode610 and the second ohmic layer 620 may vertically overlap each other. Aportion of the first light modulation electrode 610 and a portion of thesecond ohmic layer 620 may vertically overlap the third light waveguidelayer 230. The second light modulation electrode 630 may verticallyoverlap the first light modulation electrode 610 and the second tofourth light waveguide layers 220, 230, and 240 below the lower cladlayer 110 in the light modulation region RG3.

Each of the first and second light modulation electrodes 610 and 630 mayinclude at least one of gold, silver, copper, aluminum, platinum,tungsten, titanium, tantalum, molybdenum, indium, nickel, chrome, ormagnesium. The second ohmic layer 620 may include a p-type semiconductormaterial. For example, the second ohmic layer 620 may include InGaAs orGaAs.

The electrode pad 611 connected to the first light modulation electrode610 may be provided. The electrode pad 611 may include metal.

The optical device according to an embodiment of the inventive conceptmay be provided by monolithically integrating the wavelength variableregion RG2 and the light modulation region RG3. In other words, in theoptical device according to the embodiment, the wavelength variableregion RG2 and the light modulation region RG3 may be provided on onesubstrate.

In describing an operation of the optical device according to theembodiment, when a voltage is applied to the first light generationelectrode 310 and the second light generation electrode 330, the firstlight waveguide layer 210 may generate light. The light generated fromthe first light waveguide layer 210 may travel along the second lightwaveguide layer 220 in the first direction D1.

The light traveled along the second light waveguide layer 220 may bereflected or resonated by the gratings 420. The light transmittedthrough the gratings 420 may have a specific peak wavelength.

The light transmitted through the wavelength variable region RG2 mayhave a wavelength that is varied by the wavelength conversion part WC.In particular, the heating element 410 may be heated by a voltageapplied to the heating pads 411. As the heating element 410 is heated,the upper clad layer 120, the second light waveguide layer 220, thelower clad layer 110, and the gratings 420 in the wavelength variableregion RG2 may be heated. As the upper clad layer 120, the second lightwaveguide layer 220, the lower clad layer 110, and the gratings 420 inthe wavelength variable region RG2 are heated, a refractive index ofeach of the upper clad layer 120, the second light waveguide layer 220,the lower clad layer 110, and the gratings 420 in the wavelengthvariable region RG2 may be varied, and the peak wavelength of the lighttransmitted through the wavelength variable region RG2 may be varied.According to an operation condition of the wavelength conversion partWC, a variation degree of the peak wavelength of the light transmittedthrough the wavelength variable region RG2 may be changed. Here, therefractive index that is varied as the heating element 410 is heated mayrepresent an effective refractive index. The effective refractive indexmay be linearly varied according to the Bragg condition as in[mathematical equation 1] below.λ=2n _(eff)Λ  [Mathematical equation 1]

In the above [mathematical equation 1], λ, is a wavelength of light,n_(eff) is an effective refractive index, and A is a frequency ofgratings.

Referring to FIG. 1D, the light transmitted through the second lightwaveguide layer 220 may be transmitted through the third light waveguidelayer 230 and the fourth light waveguide layer 240. A joining point JPand a diverging point DP may be defined by the second to fourth lightwaveguide layers 220, 230, and 240. The joining point JP may be a pointat which the second light waveguide layer 220 and the third lightwaveguide layer 230 are connected to each other. The diverging point DPmay be a point at which the third light waveguide layer 230 and thefourth light waveguide layer 240 are connected to each other.

At the diverging point DP, the light transmitted through the secondlight waveguide layer 220 may be diverged to the third light waveguidelayer 230 and the fourth light waveguide layer 240. A ratio diverged tothe third light waveguide layer 230 and the fourth light waveguide layer240 may be about 1:1. The light diverged to the fourth light waveguidelayer 240 may be emitted to the outside of the light modulation regionRG3. The light diverged to the third light waveguide layer 230 may becompletely transmitted through the third light waveguide layer 230 andbe joined with light transmitted through the second light waveguidelayer 220 at the joining point JP, and be diverged again at thediverging point DP.

As a result, an intensity of light emitted to the outside through thefourth light waveguide layer 240 may be modulated. In other words, as avoltage is applied to the first light modulation electrode 610 and thesecond light modulation electrode 630, the refractive index of each ofthe upper clad layer 120, the third light waveguide layer 230, and thelower clad layer 110 may be varied, and a time for light transmittedthrough the third light waveguide layer 230 may be varied. Thus, theintensity of light emitted to the outside through the fourth lightwaveguide layer 240 may be modulated.

FIG. 2A is a view representing a light intensity of first light. FIG. 2Bis a view representing a light intensity of second light. FIG. 3A is aview representing a light intensity spectrum of the first light. FIG. 3Bis a view representing a transmission ratio between the first light andthe second light.

In the below description on FIGS. 2A, 2B, 3A, and 3B, light generated inthe light generation region RG1 and transmitted through the wavelengthvariable region RG2 is defined as first light P1, and when the firstlight P1 is transmitted through the light modulation region RG3 and thenemitted, the emitted light is defined as second light P2. Also, a casein which a wavelength is not varied by the wavelength conversion part WC(i.e., a case in which the wavelength conversion part WC is notoperated) is defined as a first case C1, and a case in which awavelength is varied by the wavelength conversion part WC is defined asa second case C2.

Referring to FIG. 2A, the first light P1 transmitted through thewavelength variable region RG2 may have a constant light intensityaccording to time.

Referring to FIG. 2B, the second light emitted from the light modulationregion RG3 may have a light intensity that is not constant according totime. Particularly, in the second light P2, a time at which a lightintensity is relatively great and a time at which a light intensity isrelatively small may be alternately repeated. The second light P2 mayhave a “1” signal at the time at which a light intensity is relativelygreat and a “0” signal at the time at which a light intensity isrelatively small.

As a result, the light intensity of the first light P1 may be modulatedwhen the first light P1 is transmitted through the light modulationregion RG3.

Referring to FIG. 3A, a light intensity spectrum of the first light P1in the first case C1 and the second case C2 may be checked.

In the first case C1, the first light P1 may have a peak wavelength of afirst wavelength λ1.

In the second case C2, the first light P1 may have a peak wavelength ofa second wavelength λ2.

As a wavelength of light transmitted through the wavelength variableregion RG2 is varied according to an operation of the wavelengthconversion part WC, a light intensity peak may be converted from thefirst wavelength λ1 to the second wavelength λ2.

A difference between the first wavelength λ1 to the second wavelength λ2may be defined as a first wavelength difference D1. The first wavelengthdifference D1 may be defined as a wavelength division multiplexing (WDM)grid.

Referring to FIG. 3B, a Y-axis represents a transmission ratio T betweenthe first light P1 and the second light P2. The transmission ratio T ofthe Y axis is a dB value obtained by dividing a light intensity of thesecond light P2 by a light intensity of the first light P1.

Referring to FIG. 3B, the transmission ratio T in the first case C1 andthe second case C2 may be checked. In the first case C1 and the secondcase C2, the transmission ratio T may periodically have a minimum valueaccording to the wavelength. For example, in the first case C1, thetransmission ratio T may have a minimum value at the third wavelengthλ3, a fourth wavelength λ4, and a fifth wavelength λ5, and, in thesecond case C2, the transmission ratio T may have a minimum value at thesixth wavelength λ6, a seventh wavelength λ7, and an eighth wavelength8.

A wavelength difference between the third and fourth wavelengths λ3 andλ4, a wavelength difference between the fourth and fifth wavelengths λ4and λ5, a wavelength difference between the sixth and seventhwavelengths λ6 and λ7, and a wavelength difference between the seventhand eighth wavelengths λ7 and λ8 may be the same as each other. Theabove wavelength differences may be defined as a second wavelengthdifference D2. The second wavelength difference D2 may be defined as afree spectral range (FSR).

In the third wavelength λ3, a difference between the transmission ratioT of the first case C1 and the transmission ratio T of the second caseC2 may be defined as a first extinction ratio ER1, and, in the fourthwavelength λ4, a difference between the transmission ratio T of thefirst case C1 and the transmission ratio T of the second case C2 may bedefined as a second extinction ratio ER2. When an integer multiple ofthe second wavelength difference D2 in FIG. 3B is the same as the firstwavelength difference in FIG. 3A, the first extinction ratio ER1 may bethe same as the second extinction ratio ER2. In other words, an integermultiple of the FSR is the same as the WDM grid, the first extinctionratio ER1 may be the same as the second extinction ratio ER2. When thefirst extinction ratio ER1 is the same as the second extinction ratioER2, a constant light modulation characteristic may be obtained.

The second wavelength difference D2 may be determined according to[mathematical equation 2] below.D2=c/(nL)  [Mathematical equation 2]

In the [mathematical equation 2], c is a speed of light, n is a grouprefractive index of the third light waveguide layer 230, and L is acircumference of the third light waveguide layer 230. The circumferenceof the third light waveguide layer 230 may be a circumference of avirtual closed curve (a dotted line in FIG. 1D) disposed at a centralportion between an outer surface 231 and an inner surface 232 of thethird light waveguide layer 230.

The integer multiple of the second wavelength difference D2 may be thesame as the first wavelength difference D1, and the first extinctionratio ER1 may be the same as the second extinction ratio ER2 byappropriately adjusting the group refractive index n and thecircumference L.

FIG. 4 is a view representing a simulation result of a transmissionratio according to a specific condition.

Referring to FIG. 4, when a simulation is performed in a condition inwhich a circumference of the third light waveguide layer 230 is about902.45 a group refractive index n of the third light waveguide layer 230is about 3.7, widths of the third light waveguide layer 230 and thefourth waveguide layer 240 are equal to each other, and a loss of thethird light waveguide layer 230 is about 3 cm-1, light having atransmission ratio T having a FSR of about 0.72 nm may be emitted.

FIG. 5A is a plan view illustrating an optical device according to anembodiment of the inventive concept. FIG. 5B is a cross-sectional viewtaken along line A-A′ of FIG. 5A. The optical device according to theembodiment is similar to the optical device according to FIGS. 1A, 1B,1C, and 1D except for description below.

Referring to FIGS. 5A and 5B, the optical device according to theembodiment may include a waveguide path 100 including a first wavelengthvariable region RG2 and a second wavelength variable region RG4. Thefirst and second wavelength variable regions RG2 and RG4 may be disposedat both sides of a light generation region RG1, respectively.

Gratings 420 provided in each of the first and second wavelengthvariable regions RG2 and RG4 may be arranged at a constant distance.Three gratings 420, which are arranged relatively close to each other,may be defined as a grating group G420. A distance between gratings 420in one grating group G420 may be a first distance L1. A distance betweenthe adjacent grating groups G420 may be a second distance L2. The seconddistance L2 may be greater than the first distance L1. The gratings 420provided in each of the first and second wavelength variable regions RG2and RG4 may be defined as sampled gratings.

In the optical device according to the embodiment, light generated fromthe light generation region RG1 may be reflected and resonated by thegrating groups G420 of the first and second wavelength variable regionsRG2 and RG4. Light transmitted through the first wavelength variableregion RG2 may have a specific peak wavelength.

FIG. 6A is a plan view illustrating an optical device according to anembodiment of the inventive concept. FIG. 6B is a cross-sectional viewtaken along line A-A′ of FIG. 6A. The optical device according to theembodiment is similar to the optical device according to FIGS. 5A and 5Bexcept for description below.

Referring to FIGS. 6A and 6B, the optical device according to theembodiment may include a first waveguide path 100 and a second waveguidepath 700. The first waveguide path 100 may include a light generationregion RG1, a first wavelength variable region RG2, and a secondwavelength variable region RG4. The second waveguide path 700 may bedefined as a light modulation region RG3.

The second waveguide path 700 may include a material that is differentfrom that of the first waveguide path 100. The first waveguide path 100may include a compound semiconductor, and the second waveguide path 700may include a group semiconductor. For example, the first waveguide path100 may include InP, and the second waveguide path 700 may include Si orGe. In the optical device according to the embodiment, the firstwavelength variable region RG2 and the light modulation region RG3 maybe hybrid-integrated with each other. In other words, the optical deviceaccording to the embodiment may be manufactured by coupling a substrateon which the first wavelength variable region RG2 is provided and asubstrate on which the light modulation region RG3 is provided.

FIG. 7 is a cross-sectional view illustrating an optical deviceaccording to an embodiment of the present invention. The optical deviceaccording to the embodiment is similar to the optical device accordingto FIGS. 1A, 1B, 1C, and 1D except for description below.

Referring to FIG. 7, the optical device according to the embodiment mayinclude a wavelength conversion part WC disposed on a wavelengthvariable region RG2, and the wavelength conversion part WC may include awavelength variable electrode 430 and a third ohmic layer 440. The thirdohmic layer 440 may be provided on an upper clad layer 120 in thewavelength variable region RG2, and the wavelength variable electrode430 may be provided on the third ohmic layer 440.

The wavelength variable electrode 430 may include at least one of gold,silver, copper, aluminum, platinum, tungsten, titanium, tantalum,molybdenum, indium, nickel, chrome, or magnesium The third ohmic layer440 may include a p-type semiconductor material. For example, the thirdohmic layer 440 may include InGaAs or GaAs.

A second light generation electrode 330 may extend from a lightgeneration region RG1 to a light modulation region RG3. A portion of thesecond light generation electrode 330 may vertically overlap a secondlight waveguide layer 220, the wavelength variable electrode 430, andthe third ohmic layer 440. Another portion of the second lightgeneration electrode 330 may vertically overlap a third light waveguidelayer 230 and a fourth light waveguide layer 240.

In the optical device according to the embodiment, a refractive index ofeach of an upper clad layer 120, a second light waveguide layer 220,gratings 420, and a lower clad layer 110 may be varied, and a wavelengthof light transmitted through the wavelength variable region RG2 may bevaried by a voltage applied to the wavelength variable electrode 430 andthe second light generation electrode 330.

FIG. 8A is a plan view illustrating an optical device according to anembodiment of the inventive concept. FIG. 8B is a cross-sectional viewtaken along line A-A′ of FIG. 8A. The optical device according to theembodiment is similar to the optical device according to FIGS. 1A, 1B,1C, and 1D except for description below.

Referring to FIGS. 8A and 8B, the optical device according to theembodiment may include a first light modulation electrode 610 having aring shape and a second ohmic layer 620 having a ring shape.

In terms of a planar view according to FIG. 8A, each of the first lightmodulation electrode 610 and the second ohmic layer 620 may have a ringshape. In other words, in terms of the planar view according to FIG. 8A,each of the first light modulation electrode 610 and the second ohmiclayer 620 may have a doughnut shape.

The first light modulation electrode 610 and the second ohmic layer 620may vertically overlap each other. The first light modulation electrode610 and the second ohmic layer 620 may vertically overlap a portion of athird light waveguide layer 230. Also, the first light modulationelectrode 610 and the second ohmic layer 620 may vertically overlap aportion of a second light modulation electrode 630.

The optical device according to the embodiment of the inventive conceptmay emit the light having the constant light modulation characteristicby including the wavelength variable region and the light modulationregion.

Although the exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one ordinary skilled in the art within thespirit and scope of the present invention as hereinafter claimed.Therefore, the embodiments described above include exemplary in allrespects and not restrictive, but it should be understood.

What is claimed is:
 1. An optical device comprising: a waveguide pathcomprising a light generation region, a wavelength variable region, anda light modulation region; a first light waveguide layer provided in thelight generation region to generate light; a second light waveguidelayer provided in the wavelength variable region and connected to thefirst light waveguide layer; a ring-shaped third light waveguide layerprovided in the light modulation region and connected to the secondlight waveguide layer; first and second light generation electrodesspaced apart from each other with the light generation regiontherebetween, and first and second light modulation electrodes spacedapart from each other with the light modulation region therebetween,wherein the light generation region, the wavelength variable region, andthe light modulation region are sequentially arranged in a firstdirection extending parallel to the waveguide path, wherein the firstlight generation electrode, the first light waveguide layer, and thesecond light generation electrode overlap each other in a seconddirection perpendicular to the first direction, and wherein the firstlight modulation electrode, the third light waveguide layer, and thesecond light modulation electrode overlap each other in the seconddirection.
 2. The optical device of claim 1, further comprising gratingsprovided in the wavelength variable region.
 3. The optical device ofclaim 2, wherein the second light waveguide layer extends in the firstdirection, and the gratings are arranged in the first direction.
 4. Theoptical device of claim 1, further comprising an ohmic layer disposedbetween the first light modulation electrode and the light modulationregion.
 5. The optical device of claim 1, further comprising awavelength conversion part disposed on the wavelength variable region.6. The optical device of claim 5, wherein the wavelength conversion partcomprises a heating element.
 7. The optical device of claim 5, wherein apeak wavelength of the light is converted from a first wavelength to asecond wavelength by the wavelength conversion part, a differencebetween the first wavelength and the second wavelength is defined as afirst wavelength difference, a free spectral range (FSR) of the lightemitted from the light modulation region is defined as a secondwavelength difference, and an integer multiple of the second wavelengthdifference is the same as the first wavelength difference.
 8. Theoptical device of claim 7, wherein the second wavelength differencesatisfies a mathematical equation below:second wavelength difference=c/nL  [Mathematical equation] in the abovemathematical equation, c is a speed of light, n is a group refractiveindex of the third light waveguide layer, and L is a circumference ofthe third light waveguide layer.